As a method for immunologically detecting an analyte in a sample, immunochromatography is known. Immunochromatography is a method for detecting an analyte by an antigen-antibody reaction by using a test strip. In immunochromatography, an antibody or antigen fixed on the chromatography membrane, the analyte, and antibody or antigen bound to a labeling marker (labeled antibody or labeled antigen) are made reacted on the chromatography membrane on which the antibody or antigen has been fixed in a detection zone.
At the time when an analyte is detected by utilizing an immunochromatography, even a negative sample in which the analyte is not contained in a sample may be determined as a positive (false-positive) in some cases. As a causing factor of false-positive, it is estimated that a labeled antibody or labeled antigen is nonspecifically bound to the detection zone. In order to suppress false-positive by such a nonspecific reaction, a blocking material is used (Japanese Laid-Open Patent Publication No. 10-068730). According to this technology, after an antibody or antigen has been fixed on the chromatography membrane, the nonspecific reaction can be suppressed by immersing the chromatography membrane in a buffer containing the blocking material, and further drying. However, in the case where a chromatography membrane having multiple detection zones for detecting two or more types of analytes is used, even if the above-described technology is used, a nonspecific reaction can be generated, and resulted in false-positive. This is because the substance fixed on the detection zone located on the side of upstream of the development direction is trapped in the detection zone located on the side of downstream separated from the detection zone. Therefore, the development of a test strip in which a false-positive is not generated by a nonspecific reaction in the detection zone located on the side of downstream has been desired.